Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-06-29
2002-02-19
Negash, Kinfe-Michael (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200
Reexamination Certificate
active
06348986
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to wireless telecommunications networks, and more particularly to a broadband telecommunication system and network which employs atmospheric (i.e. free-space) laser transmission.
DESCRIPTION OF THE RELATED ART
In the modern telecommunications market, there exists a vast array of products and services targeted for the needs and desires of consumers at every level. Many of these products and services necessitate a network infrastructure. For example, telephone service is mediated by the Public Switched Telephone Network (PSTN), also known as the Plain Old Telephone System (POTS).
Any-to-any connectivity is a fundamental organizing principle of the PSTN, i.e. any telephone subscriber should be able to call and communicate with any other telephone subscriber. The switching systems employed in the PSTN are almost completely digital. Fiber optic cables, copper cables, microwave links, and satellite links are used for data transmission. Transmission over the local loop is typically carried by copper-based T
1
feeder or fiber optic cable. However the subscriber loop is still primarily implemented with copper UTP (unshielded twisted pair). Thus, the transmission bandwidth deliverable to a telephone subscriber is severely limited, typically less than 56,600 bits per second. At present, the PSTN bears the triple burden of conveying voice, fax, and data communications, and is nearly saturated in certain large metropolitan regions.
The Integrated Services Digital Network (ISDN) represents a step upward in speed relative to the PSTN. First time subscribers to ISDN service generally incur a cost for installation of an ISDN line which comprises upgraded copper wire. Computer users who access a corporate Intranet or the Internet through an ISDN line and ISDN modem experience increased performance relative to connecting through the PSTN.
A variety of communication applications such as interactive television, video telephony, video conferencing, video messaging, video on demand, high definition television (HDTV) and high-speed data services require broadband data transmission. In fact, many communication applications may require bandwidths high enough to exclude ISDN as a feasible medium for establishing a data connection.
Optical fiber offers significantly higher data transmission bandwidths than copper wire/media. However, fiber optic networks such as fiber to the curb (FTTC) and fiber to the home (FTTH) require new fiber optic cable to be run to every subscriber. Thus, the cost of implementing a fiber optic network may be exorbitant. Other alternatives for increasing the capacity of existing networks include Asymmetric Digital Subscriber Line (ADSL), Symmetric Digital Subscriber Line (SDSL), and Hybrid Fiber Coax (HFC), among others.
In general, all hard-wired networks are burdened with the requirement of laying cable to new subscribers
odes. Furthermore, it is difficult to reconfigure the topology of an existing hard-wired network since cables are quite often buried underground, suspended from poles, or stung through the interstitial spaces of office buildings.
In contrast, wireless networks based on the radiation of electromagnetic energy through free space (i.e. the atmosphere) are able to service subscribers without incurring costs for laying cable to the subscribers. Many wireless telecommunication systems are organized as broadcast systems where a single transmitter sends an information signal to multiple receivers. For example, the Direct Broadcast Satellite (DBS) systems such as PrimeStar, Digital Satellite Service, etc. provide satellite broadcast of video channels to subscribers equipped with a receiving antenna (typically a dish antenna) and a set-top decoder. Wireless telecommunication systems and networks are widespread and numerous. Their numbers continues to increase in response to consumer demand. Thus, the radio spectrum is increasingly crowded resulting in degraded signal quality and/or increased subscriber costs.
In certain circumstances and for various reasons, a client/customer may desire point-to-point communication, i.e. the transmission of information between two points separated by a distance. For example, a microwave link between two central offices in the PSTN may be a point-to-point connection. Laser technology provides an admirable alternative to radio transmission for establishing broadband point-to-point communication due to the fact that lasers inherently generate narrowly focussed beams. Laser-based wireless systems have been developed for establishing point-to-point, bi-directional and high speed communication through the atmosphere. The range for such systems is typically 0.5 to 1.2 miles, with some systems achieving a range of 4 miles or more. The longest atmospheric communication path achieved with a point-to-point system exceeded 100 miles.
These point-to-point systems require a laser-based communication unit at each end of the point-to-point connection. A laser-based communication unit includes an optics package, a laser transmitter, an optical receiver, and a data interface package. The laser transmitter includes a laser for generating a laser beam, and modulating electronics for impressing a first information signal onto the laser beam. Quite often, the first information signal is a digital signal and ON/OFF keying is employed as the modulation scheme. The modulated laser beam is transmitted into the atmosphere by the optics package. Thus, the optics package is sometimes referred to as an optical antenna. The optics package also receives a second laser signal from the atmosphere, and provides the second laser signal to the optical receiver. The optical receiver includes photo-detection and demodulation electronics for recovering a second information signal from the second laser signal.
The data interface package is coupled to the laser transmitter, the optical receiver and to a communication bus. The data interface package is configured to send and receive data on the communication bus according to a pre-defined communication protocol. The data interface receives the first information signal from the communication bus and transmits the first information signal to the laser transmitter for modulation. The data interface also receives the second information signal from the optical receiver and transmits the second information signal onto the communication bus. Typically, a computer of some sort generates the first information signal and receives the second information signal. Thus, the computer generally requires a separate interface card/package in order to send/receive signals over the communication bus. For example, the communication bus may be the well-known Ethernet bus. In this case, the data interface in the laser-based communication unit is Ethernet compatible as is the interface card/package coupled to the computer.
In prior art laser-based point-to-point systems, the subsystems of the laser-based communication unit, i.e. the optics package, the laser transmiitter, the optical receiver, and the data interface package, are physically integrated into a common chassis. As will become apparent in the following discussion, the binding of all the sub-systems into a commnon chassis effects the design complexity of the communication unit and the installation procedures for the communication unit both of which impact the effective cost to the consumer.
In order to establish a point-to-point connection, two laser-based communication units must be configured so that their respective optical antennas achieve a line of sight (LOS) through the atmosphere. This generally requires that the units be installed at an elevated outdoor location such as a rooftop. Since, the communication unit includes active electronics, the user/client generally incurs a significant cost for providing a power connection to the installation site. This cost severely impacts the marketability of existing laser-based systems to home users and small business users.
The communication unit, being situated out of doors, may
Doucet Mark A.
Panak David L.
Brightwell Mark K.
Conley Rose & Tayon PC
Dominion Lasercom. Inc.
Hood Jeffrey C.
Negash Kinfe-Michael
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